Calorimetric Analysis of the Effect of Streptomycin, Tetracycline and Chloramphenicol on the Growth of Escherichia coli

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The effects of streptomycin, tetracycline and Chloramphenicol on the growth of Escherichia coli were studied quantitatively in a conduction-type batch calorimeter at pH 6.2 and 37°C. Change in the growth thermograms with increasing drug concentrations in the medium were analyzed with a kinetic model of non-competitive inhibition.
The number of drug molecules needed to inactivate a unit viable cell, m, was estimated to be 1.2±0.1, 0.7±0.1 and 1.3±0.1 for streptomycin, tetracycline and Chloramphenicol, respectively. With the assumption that the drug binding sites are all identical, the microscopic dissociation constant per binding site, K_i for the drugs was found to be 0.19, 0.43 and 0.94 μmol dm^-3 for streptomycin, tetracycline and Chloramphenicol, respectively. With these m and K_i values, drug potency curves were drawn for the three drugs.